This invention relates to loudspeakers and, more particularly, to horn loaded loudspeakers.
The range of hearing for a young person typically includes sound frequencies having wavelengths from approximately 20 Hz to approximately 20 kHz. The upper limit typically falls with age to approximately 10-15 kHz. In speaker design, ideally one would like to have a single speaker that could faithfully reproduce sound over the full range of audible wavelengths. This is generally considered impractical, in part because different loudspeaker characteristics are desirable for reproducing sound at different wavelengths. For example, it is typically desirable to have a driver diaphragm that less mass at higher frequencies and more mass at lower frequencies.
Similarly, it is typically desirable to have a driver magnet having less mass for reproducing sounds at lower frequencies and having more mass for reproducing sounds at higher frequencies.
Because of the different properties that are desirable for reproducing sound waves having different frequencies, different drivers are typically used for reproducing different ranges of frequencies. For example, a sub-woofer may be used to reproduce sound waves having a frequencies of approximately 80-100 Hz or less. A woofer is typically used to reproduce sound waves having frequencies from approximately 80 Hz to approximately 400 or 800 Hz; some woofers are being used to reproduce sound waves having frequencies of as high as approximately 1200 Hz. Mid range drivers are typically used to reproduce sounds from approximately 300 Hz to approximately 7 kHz, and tweeters are typically used to reproduce sounds from approximately 1500 Hz to approximately 20 kHz.
Loudspeakers using horn loading or using a bass reflex system are known in the art, each design offering its own advantages and disadvantages. In a horn loudspeaker, a horn is typically an angled or curved tube with a gradually increasing cross section area that shapes and directs sound radiating from the horn. A horn is typically made of metal, plastic or wood. In designing a horn for a loudspeaker, the curvature of the horn side walls is typically determined using a selected mathematical equation or formula depending upon the desired characteristics of the loudspeaker. Horn loaded loudspeakers offer a number of advantages. For example, a horn loaded speaker, in which a horn is placed in front of a driver, such as a woofer, is a highly efficient speaker, providing relatively high sound pressure levels with relatively low power input. To better understand the improved efficiency and the directivity of a horn loaded loudspeaker, it may be helpful to visualize the effect a megaphone has on cheers or instructions shouted or spoken into it. If the horn is well designed, the horn loaded speaker also offers a smooth frequency response. Although they offer many advantages, horn loaded speakers are not without problems. When the size of the loudspeaker is a concern, a horn loaded speaker is relatively large, particularly when the speaker is designed to extend into lower frequencies.
In a bass reflex or vented box type system, a vent is added to a closed box that typically has a direct radiation driver, and the vent is tuned so that the sound radiating from the vent effectively adds to the direct sound from the driver. A bass reflex system provides good low frequency extension, improving the driver response near the low cut-off frequency, particularly for woofers. Venting such as is done in a bass reflex system provides the most benefits for drivers reproducing low frequency sound waves and does not provide as significant benefits for drivers reproducing higher frequency sound waves such as tweeters and mid-range drivers. When size is of concern, a relatively small bass reflex system can offer good performance, particularly for a speaker designed to extend into lower frequencies. A bass reflex system, however, is relatively inefficient and has higher distortion than a well-designed horn loaded system.